Antibiotic Susceptibilities of Pseudomonas aeruginosa Isolates Derived from Patients with Cystic Fibrosis under Aerobic, Anaerobic, and Biofilm Conditions

Abstract

Recent studies have determined that Pseudomonas aeruginosa can live in a biofilm mode within hypoxic mucus in the airways of patients with cystic fibrosis (CF). P. aeruginosa grown under anaerobic and biofilm conditions may better approximate in vivo growth conditions in the CF airways, and combination antibiotic susceptibility testing of anaerobically and biofilm-grown isolates may be more relevant than traditional susceptibility testing under planktonic aerobic conditions. We tested 16 multidrug-resistant isolates of P. aeruginosa derived from CF patients using multiple combination bactericidal testing to compare the efficacies of double and triple antibiotic combinations against the isolates grown under traditional aerobic planktonic conditions, in planktonic anaerobic conditions, and in biofilm mode. Both anaerobically grown and biofilmgrown bacteria were significantly less susceptible (P < 0.01) to single and combination antibiotics than corresponding aerobic planktonically grown isolates. Furthermore, the antibiotic combinations that were bactericidal under anaerobic conditions were often different from those that were bactericidal against the same organisms grown as biofilms. The most effective combinations under all conditions were colistin (tested at concentrations suitable for nebulization) either alone or in combination with tobramycin (10 g ml ؊1 ), followed by meropenem combined with tobramycin or ciprofloxacin. The findings of this study illustrate that antibiotic sensitivities are dependent on culture conditions and highlight the complexities of choosing appropriate combination therapy for multidrug-resistant P. aeruginosa in the CF lung.

A Winogradsky-based culture system shows an association between microbial fermentation and cystic fibrosis exacerbation

“…Thus conventional culture on microbiological media misses important components of the CF microbial community that may contribute to exacerbations and provides antibiotic resistance profiles from microbes not grown in a state in which they cause disease. For example, Pseudomonas aeruginosa has very different antimicrobial susceptibilities under aerobic, anaerobic or biofilm growth (Hill et al, 2005;King et al, 2010). Growth of clinical samples in an environment more similar to the CF lung would provide better information and more predictable treatment outcomes.…”

Molecular Detection of blaVEB-1 Beta-Lactamase Encoding Gene Among Extended Spectrum B-Lactamase Positive Wound Isolates of Pseudomonas aeruginosa

“…In the study of Kapur from India, 61% of urinary tract pathogens were ESBL positive (26). For resistant isolates combination therapy (usually including a class of β-lactam and an aminoglycoside) is recommended that would contribute to the curing of pseudomonal infections (27). Less than half of our wound isolates of P. aeruginosa produced ESBLs among which an approximate half could amplify the bla VEB-1 gene.…”

Is there value in susceptibility testing ofPseudomonas aeruginosacausing chronic infection in patients with cystic fibrosis?

“…The reason for this is that tobramycin, a comparatively large, highly charged molecule, can only enter bacteria through active transport. The energy required to drive this transport is derived during oxidative phosphorylation, which does not occur in anaerobically growing organisms [19]. As a result, an organism reported to be susceptible to tobramycin in vitro may not respond in vivo.…”

“…Biofilm-based susceptibility methods may be better able to predict which antimicrobials lack activity against P. aeruginosa. However, this method is limited currently to research laboratories [4,19]. Further investigation is required to determine whether or not this technique would provide better guidance than the currently used agar-based methods.…”

“…The Ottawa investigators have taken this approach one step further [19]. They have compared MCBT with organisms grown planktonically, as biofilms and anaerobically.…”